The present invention relates to a method of and an installation for the continuous production of block-foam. In the method, a reaction mixture produced from at least two foam-forming, liquid reaction components is applied to a foil conveyed on a moving support with the formation of a closed, laterally restricted layer. The reaction mixture then changes from a liquid condition into a creamy condition. Finally, the mixture completely reacts into a foam block with the resultant enlargement of the volume.
In the continuous production of block-foam, an equilibrium condition exists at the beginning of the foaming-up region. The mixture delivered to the foil rises without a relative movement parallel to the foil, to form the foam block. This equilibrium is extremely unstable because there is the danger that the applied mixture will flow under (or underscour) the mixture which has already started to foam. Additionally, even the previously applied mixture may flow back against the direction of transport. This over-rolling of differently aged reaction mixture results in faults in the final foam which are visible in the cross-section of the completely reacted foam block in the form of sections of a varying density or cell size, streaks or even cracks.
The only way of countering this over-rolling is by maintaining a certain minimum conveying speed, dependant also on the other parameters.
For this reason, small installations (i.e., those which are to operate with a low throughput) become uneconomical because a relatively long foaming zone and hardening zone must be provided for a desired block height, due to the low speed. This necessarily implies a high mechanical expense and a considerable requirement of space.
Similar difficulties arise in the case of large installations (i.e., installations with a high through-put which in particular produce blocks above the conventional height of from 1 to 1.20 m). Overrolling takes place in this case because the reaction mixture cannot be supplied in a sufficiently high, stationary layer, without the over-rolling phenomena occurring as the result of the strong flow.
To solve this problem, it has been proposed (see U.S. Pat. No. 3,786,122) to connect a trough upstream of the actual foaming region. The reaction mixture is supplied to the bottom of the trough, starts to react, and finally flows away, over a weir, into the actual foaming region. As a result of varying the height of the weir over its width, the overflow of the reaction mixture which is starting to react may be controlled so that a foam block having a rectangular cross-section forms.
However, the glass contained in the reaction mixture or gases which are produced by the reaction itself cannot penetrate the mixture column towards its outer surface during this intermediate storage of the reaction mixture in the trough, because the reaction mixture which is on the surface has already reacted to such an extent that it has too high a viscosity. Consequently, gas bubbles remain in the initially reacted mixture, and can no longer escape. This will necessarily finally adversely affect the homogeneity of the finished block.
According to another proposal (U.S. Pat. No. 4,005,958), the flow of a mixture which is applied as a film and is still in a liquid condition is braked by several retaining weirs. Each weir forms an overflow, in front of which mixture builds up so that the individual particles of mixture have a different residence time in each build-up. In particular, there is also the danger of the reaction mixture flowing back on the surface, so that the age spectrum of the mixture is widened to an even greater extent. The disturbances which have been mentioned and inferior physical properties of the foam also occur as a result of this. A disadvantage is also seen in the fact that the base foil cannot be guided over the weirs. After each standstill, the zone of the retaining weirs has to be cleaned of completely reacted reaction mixture.
Thus, the object of the present invention is to continuously produce block-foam by a suitable method in an installation which is designed for either low throughput or a high throughput and in particular for the production of high blocks, to obtain a product having a homogeneous foam structure, i.e. a streak-, crack- and bubble-free product which has optimum physical properties.